1. Field of the Invention
The present invention relates to a driving circuit of a plasma display panel, and more particularly, to a driving circuit of a plasma display panel which uses one energy recovery unit for charging and discharging both sides of a panel capacitor.
2. Description of the Prior Art
In recent years, plasma display panels (PDP) have become more and more popular over the traditional cathode ray tube terminals (CRT) due to the advantages of thinner appearance and higher quality display. Generally speaking, under a given voltage, charges accumulated over electrodes in a PDP are released to produce discharge glow that can achieve different display effects. PDPs can be categorized into two types depending on driving method. The first type is an alternating current (AC) PDP operated by an AC discharge indirectly between electrodes coated with dielectric film. The second type is a direct current (DC) PDP operated by a DC discharge directly between electrodes exposed to a discharge space. The AC PDP has been regarded as mainstream because of lower power consumption and longer lifetime.
A customary surface-discharge AC type PDP is composed of a display panel and a driving circuit. The PDP includes a plurality of discharge units, each having paired electrodes, an X-electrode and a Y-electrode, and an address electrode. The driving circuit is for driving the three electrodes of each discharge unit respectively, in accordance with the driving method and the driving procedures. The typical operation of an AC plasma display involves applying alternating pulses to paired electrodes in order to initiate discharge glow. A voltage of up to about 200 V is typically required to be applied to the electrodes. In addition, a pulse-duration of several microseconds is usually adopted. Hence the power consumption of the PDP display is quite considerable. Energy recovery (power saving) is therefore sought. Many designs and patents have been developed for providing methods and apparatuses for energy recovery in PDPs. One of the examples is U.S. Pat. No. 4,866,349 “Power Efficient Sustain Drivers And Address Drivers for Plasma Display Panel” to Weber et al., which is included herein by reference.
FIG. 1 is a circuit diagram showing an example of a prior art PDP driving circuit 10. As shown, the driving circuit 10 comprises an X-side driving circuit section 11 and a Y-side driving circuit section 12 having the same structure as the X-side driving circuit section 11. The two driving circuit sections 11 and 12 are coupled to each other in series by a panel capacitor 14. Here, the construction and operation of only the X-side driving circuit section 11 will be described.
In the X-side driving circuit section 11, an inductor 16 is connected to an X-side of the panel capacitor 14 (In the Y-side driving circuit section 12, the inductor 16 is connected to a Y-side of the panel capacitor 14). Four field-effect transistor (FET) switches 21, 22, 23 and 24 are connected to the ends of the inductor 16. A recovery capacitor 29 is connected commonly to one end of each of the two FET switches 21 and 22 and serves as a variable voltage source, which varies according to the value of Vs, for the driving circuit 10. Designated as D are diodes.
In the X-side driving circuit section 11, a series resonance is caused between the inductor 16 and the panel capacitor 14, and the panel capacitor 14 is charged and discharged during one half of the resonance period. Meanwhile, a voltage of about one half the value of the voltage VS, which charges the panel capacitor 14, is applied externally, whereby energy used when charging and discharging the panel capacitor 14 with a single X-electrode pulse (or a single Y-electrode pulse in the Y-side driving circuit section 12) is recovered at the recovery capacitor 29 so as to be used when charging the panel capacitor 14 with the next X-electrode pulse. This reduces power required to be newly supplied from the source line VS.
FIG. 2 is a pulse waveform chart describing operation of the driving circuit 10. A waveform A is of the X electrode pulse at the X-side of the panel capacitor 14. A waveform B is of the Y electrode pulse at the Y-side of the panel capacitor 14. A waveform C is a resultant waveform produced from the waveform A and the waveform B to facilitate the understanding of the operation between the surface discharging electrodes. Time Tf is the pulse fall time, and time Tr is the pulse rise time.
In the above prior art plasma display panel driving circuit 10, both the X electrodes and Y electrodes of the plasma display panel require independent circuits: the driving circuit section 11 and the driving circuit section 12. Besides, as the number of driving electrodes increases with increasing panel size, the number of necessary circuits is also increased thus increasing the total number of devices involved. Hence the power consumption and the required circuit space of the prior art PDP driving circuit are quite considerable.